The King Power Racing-owned four-year-old won three times at York last season, including a Group One triumph in the Nunthorpe in August.
And while she subsequently failed to fire in either the Flying Five at the Curragh or the Prix de l'Abbaye at ParisLongchamp, hopes were high ahead of her reappearance in the Group Two Temple Stakes.
But after racing prominently for much of the five-furlong contest, Winter Power weakened tamely and passed the post eighth of the 10 runners, with Easterby putting the performance down to a lack of match fitness.
"She's fine. She's come out of it sound and well," said the North Yorkshire-based trainer.
"She just had a blow and needed the race, but she seems all right.
"That (King's Stand) is the idea."
When asked if Winter Power could run again before the Royal meeting, Easterby added: "I wouldn't have thought so, but you never know."